Big Energy Savings, Recycling in Place, Reduced Heat Island Effect: Why the World Is Warming Up to Cool Roofing
Globally, more people live in urban than rural areas. Between continued population growth and urbanization, the world’s cities can expect to house about 2.5 billion more people by 2050. Having so many people living and working close together in a built environment can cause the temperature of a city to rise—creating what is called the “urban heat island effect.” The difference can be as high as 22 degrees Fahrenheit at night, increasing energy demand for cooling, and raising air pollution and greenhouse gas emission levels.
One factor that can dramatically reduce the heat island effect is “cool roofing”—or a roof with high solar reflectance. Cool roofs have been around for more than 30 years and, in addition to helping to reduce the heat island effect, they reduce interior building temperatures, saving energy used for air conditioning and keeping building occupants more comfortable.
Another great benefit of cool roofs is that they can often be applied over existing flat and low-slope roofs, extending the roof’s life and reducing the need for tear-off and disposal. This is known in the field as “recycling in place.”
What Is Cool Roofing?
Cool roofing for retrofit applications typically utilizes a thick (more than 0.5 millimeters), white, monolithic, solar-reflective elastomeric coating—made from either acrylic, silicone, or polyurethane resins—that is applied on top of multilayered flat or low-sloped roofing systems. In addition to reflecting sunlight, the coating provides some protective and energy management properties. It can be applied with a roller, brush, or sprayer.
Energy savings from cool roofs vary depending on local climate conditions, the building’s operating system and internal conditions, the roof surface area, and the building’s roof assembly design and construction. Dow (or its subsidiaries) has been conducting studies of reflective roof coatings since 1981. More recent modeling and case studies indicate cool roofs achieve average energy savings of 4.6% in Barcelona and 19.2% in Dubai. A 2004 Texas A&M study indicated savings averaging 20% in California cities.
It is estimated that in the United States alone, about 8 million tons of roofing waste ends up in landfills, taking up a substantial portion of the space. Because cool roofing can be applied directly over asphalt, single-ply, and other roofs, it can dramatically decrease landfill waste worldwide.
Raising the Profile of Cool Roofing
Cool reflective roof coatings have been recognized by the U.S. Green Building Council’s Leadership in Energy and Environmental Design as contributing to reducing the heat island effect. And companies like Dow continue to innovate to improve the technologies with advances like Dow’s recently released CENTURION™ roof binder, which uses cross-linking technology to improve elastomeric roof coating performance when water ponds on the roof.
Essentially any flat or low-sloped roof has the potential to be retrofitted with cool roofing. Demand for the technology is growing in North America. Demand is also growing in many other areas of the world—including warm climates, where the possible benefits are greatest.
Dow is collaborating with several governments, associations, and non-governmental organizations to raise the profile of cool roofing and help educate the industry about the technology and encourage its use. As more building owners and communities understand the benefits of this technology, cool roofing could become tomorrow’s hottest recycling trend.
30 Years and Counting
After struggling with bubbling and “alligatoring” of a four-ply asphalt roof on the Bakes Athletic Complex at Ursinus College in Collegeville, Pennsylvania, the roof was retrofitted with a reflective coating. Acrymax Technologies Inc. formulated the coating using Dow acrylic polymers. Thirty years later, the roof is still in good shape. With periodic recoating, the roof’s life could be extended indefinitely. The technology has since been used to extend the life of about 40 other campus buildings.